The invention relates to manufacturing and testing apparatus for thin film disks and more particularly to apparatus and methods for detecting film delamination defects in thin film disks.
A typical prior art head and disk system 10 is illustrated in FIG. 1. In operation the magnetic transducer 11 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 11, usually called a xe2x80x9cheadxe2x80x9d or xe2x80x9cslider,xe2x80x9d is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. The magnetic transducer 11 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded. The thin film protective layer (not shown in FIG. 1) is typically the last or outermost layer.
The conventional disk 16 typically has a substrate 26 of AIMg or glass. The thin films 21 on the disk 16 typically include a chromium or chromium alloy underlayer that is deposited on the substrate 26. The magnetic layer in the thin films 21 is based on various alloys of cobalt, nickel and iron. For example, a commonly used alloy is CoPtCr. However, additional elements such as tantalum and boron are often used in the magnetic alloy.
FIG. 2 illustrates one common internal structure of the thin films 21 on disk 16. The protective overcoat 35 is used to improve wearability and corrosion. The magnetic layer 34 is immediately under the overcoat 35. The magnetic layer 34 is deposited on an underlayer 33 which is in turn deposited on a seed layer 32. The seed layer 32 is deposited on the substrate 26. Since the seed layer 32 is the initial thin film deposited on the substrate 26, it plays a critical role in the adherence of the thin film structure to the substrate. For nonmetallic substrates various seed layer materials have been suggested including chromium, titanium, tantalum, CrTi, Ni3P, MgO, carbon, tungsten, AlN, FeAl, RuAl and NiAl.
One of the prior art steps in processing thin film magnetic disks has been burnishing. The burnishing process flies a special type of slider structure over the disk surface to physically remove high spots from the disk surface. U.S. Pat. No. 5,658,191 to Brezoczky describes a type of burnishing head and the process of using it.
The prior art manufacturing process for thin film disks has included various optical, magnetic and physical tests. An optical inspection system is described in U.S. Pat. No. 6,100,971 to Imaino, et al., which is commonly assigned with the present application. One physical test is called a glide test. A glide test is used to gauge the suitability of the surface of the disk for xe2x80x9cflyingxe2x80x9d the read/write (R/W) head. One prior art glide test is described in U.S. Pat. No. 6,262,572 issued to Franco, et al. A glide test using a thermo-resistive element is used to detect thermal asperities which are caused by irregularities in the surface of the disk. Franco ""572 suggests using a glide head that is much wider than an actual R/W head in order to speed up the process of testing a disk.
One of the failure mechanisms for thin film disks is delamination of the thin film structure from the substrate. In typical manufacturing procedures delaminations are often not detected until the disk is installed in and tested in the final disk drive assembly. It is clearly advantageous to detect defects on a disk prior to installation in a drive. An additional problem in delamination defect analysis is being able to locate the defect in a microscope field for failure analysis. The critical defects are not visible with the naked eye, so it can be time consuming to search for the defect using any type of high magnification device.
The applicants disclose an apparatus and method for detecting and marking delamination defects on thin film disks. The apparatus includes a read/write (R/W) head and a burnishing head mounted on separate arms that access the disk while spinning on the test stand. The R/W head performs an initial magnetic test of selected areas on the disk to establish an initial defect map. The burnish head is then flown over the surface for an extended time to accelerate and open up the latent delamination defects by impacting protruding material. The R/W head then performs a second magnetic test which is compared against the first test to identify the delamination defects which have been developed by the burnishing. The delamination defects are then marked with a magnetic pattern which aids in optically locating the defect, for subsequent failure analysis.